Mounts of the aforementioned type are used for mounting motor vehicle assemblies in order to dampen or absorb vibrations occurring during operation. In this case, the hydromount has several damping or absorbing systems that achieve a damping or absorbing effect at different excitation frequencies. For example, the suspension spring consisting of an elastomeric material effects an acoustic insulation. A damping of low-frequency vibrations with a large amplitude is carried out via the damping channel. In the process, the introduced vibrations result in a movement of the suspension spring, whereby a hydraulic pressure is built up within the working chamber. Due to the pressure, the fluid flows from the working chamber via the damping channel into the compensation chamber. Due to the small diameter of the damping channel and the high mechanical transmission associated therewith, which results from the equivalent displacing cross section of the suspension spring in relation to the damping channel cross section, the introduced vibrations are absorbed or damped.
In order to decouple high-frequency, low-amplitude vibrations, i.e. in the acoustically relevant area, the introduction of an elastic membrane with or without play within the partition is known. In this case, the membrane vibrates at high-frequency, low-amplitude vibrations, so that a damping action is decoupled via the damping channel.
Furthermore, it is known to introduce into the partition a through-hole or a channel, which can also be referred to as idling channel or absorber channel, and which can be unblocked and closed by means of a switchable actuating device, in order to reduce the dynamic bearing rigidity during the idling of the engine. Such mounts are also referred to as switchable mounts. Depending on the engine speed, the channel is opened or closed. In the case of a closed channel, the mount works like a conventional mount, in which low-frequency vibrations with high amplitudes are damped by a liquid displacement within the damping channel and high-frequency vibrations with low amplitudes are insulated or decoupled by means of the membrane. In the open position of the channel, a liquid column oscillates within the channel, so that the high-frequency engine vibrations occurring during engine idling are transmitted to the chassis in a significantly reduced form due to the small effective spring rate.
Hydromounts of this type are known from DE 43 30 560 C1 and EP 1 688 639 B1. Here, switchable hydromounts are disclosed whose idling channel can be opened or closed by means of an actuating device to which a negative pressure can be applied.
In this case, it is disadvantageous that an energy supply with negative pressure is not available in a sufficient quantity in modern motor vehicles, particularly in motor vehicles with hybrid or electric drives.
In order to circumvent this drawback, a hydromount is presented in EP 2 028 392 B1 whose actuating device is switchable via an electrically drivable electromagnet. Here, in order to form an absorber channel, an opening is introduced into a partition which is delimited in an axially downward direction by a pot-shaped support wall and an electromagnet. A partially flexible membrane, which is at least partially made from a magnetizable elastomer or provided with a metal part, extends into the absorber channel in a sack-like manner. By applying a current to the electromagnet, the membrane abuts against the support wall and the electromagnet, so that the absorber channel is inactive. In order to activate the absorber channel, the current supply to the electromagnet is interrupted. Thus, the membrane is spaced from the electromagnet and is able to vibrate with the liquid column located in the absorber channel against the vibrations introduced in the axial direction. What is disadvantageous in this case is that, due to the pot-shaped configuration of the support wall, the membrane abuts against the support wall when the absorber channel is active. As a consequence, the expanding-spring rate of the membrane is not effective. This results in a lower mechanical transmission, so that the dynamic spring rate of the hydromount in engine idling is not lowered to a sufficient extent.